Early life exposure to indoor air pollutants and the risk of neurodevelopmental delays: The Japan Environment and Children’s Study

Air pollution has been associated with childhood neurodevelopment. However, the role of indoor air pollution, especially volatile organic compounds (VOCs), on childhood neurodevelopment has been poorly explored to date. We investigated the association between indoor air pollutants and childhood neurodevelopment in 5,017 randomly selected children from the Japan Environment and Children's Study. When the participants reached 1.5 and 3 years of age, they were followed up with home visits and neurodevelopmental tests using the Ages and Stages Questionnaire (ASQ). At both ages, we collected indoor air samples for 1 week and measured 13 indoor air pollutants: particulate matter with an aerodynamic diameter of ≤2.5 μm, ozone, nitrogen dioxide, sulfur dioxide, and nine VOCs. The associations between air pollutants and ASQ scores were estimated using linear mixed effects models and weighted quantile sum regressions (WQS) at each age separately. Stratified analysis by sex was conducted. Exposure to m,p-xylene at the age of 3 was associated with lower communication, fine motor, and overall ASQ scores (coefficients: −0.18 [99% confidence intervals (CI): −0.35, −0.02], −0.23 [99 %CI: −0.43, −0.03], and − 0.72 [99 %CI: −1.41, −0.04] per 1 µg/m3 increase, respectively). Exposure to o-xylene at the age of 3 was associated with lower communication, gross motor, fine motor, and overall ASQ scores (coefficients: −0.48 [99 %CI: −0.90, −0.07], −0.45 [99 %CI: −0.78, −0.13], −0.65 [99 %CI: −1.14, −0.16], and −2.15 [99 %CI: −3.83, −0.47] per 1 µg/m3 increase, respectively). The WQS index was associated with lower gross motor ASQ scores at the age of 3 (coefficient: −0.27 [95 %CI: −0.51, −0.03] for one-unit WQS index increases), which was attributed to benzene (33.96%), toluene (26.02%), o-xylene (13.62%), and ethylbenzene (9.83%). Stratified analysis showed similar results. Although further investigations are required, our results suggest an association of neurodevelopmental delays with indoor low-level exposure to m,p-xylene and o-xylene in early life.